The proliferation and differentiation of hematopoietic cells is under the control of hematopoietic growth factors. These growth factors are produced by bone marrow stromal cells such as fibroblasts and lymphocytes. Their action on hematopoietic cells is mediated by high affinity cell surface receptors. There is substantial redundancy in the spectrum of activity of hematopoietic growth factors in that individual factors may act on mature and immature cells of several lineages and there are several factors that have overlapping spectra of activity. One approach to defining the physiologic role of an individual growth factor is to create animals deficient in their capacity to provide that factor. We are attempting to use anti-sense RNA sequences specific for the mouse granulocyte macrophage-colony stimulating factor (CM-CSF) to achieve this purpose. The coding sequences for GM-CSF are placed in a reverse transcriptional orientation under the control of a strong promoter in a expression plasmid that includes a lymphocyte specific, dominant control region. The ability of these sequences to inhibit GM-CSF production by cultured lymphocytes will be determined. If the anti-sense strategy proves effective, transgenic animals will be created containing the active transcriptional unit. The lymphocytes of such animals should lack the capacity to produce GM-CSF. Study of these transgenic animals may provide an indication as to the physiological role of GM-CSF in hematopoiesis. A second active area of investigation is directed at the mechanism of signal transduction by hematopoietic growth factors. Each growth factor induces the expression of several "early" genes the products of which are thought to lie on a signal transduction pathway. Our general strategy is to express several of these genes at high level in cells to determine whether the requirement for growth factor is abrogated. In addition, we will determine whether a cascade is operative whereby one gene product induces the expression of other genes.